Marriage between waste and clean energy

Marriage between waste and clean energy – talk by Alistair Gets at the U3A general meeting held at the Muizenberg Pavilion on the 2 Sept. 2010.

Alastair graduated from UCT as a Mechanical Engineer. As a registered Professional Engineer and Certified Manager, he has walked a path, beginning as a design engineer at a power facility and evolved into conceptual analysis in the renewable energy industry. He is a respected strategist advisor within the sustainable energy field. He has worked on energy efficiency, carbon footprints, wind, solar and especially energy from waste. He works with AGAMA ENERGY.

Alastair began by saying that in the current debate re Climate Change, there is now a generally accepted consensus that greenhouse gases produced by humans are the culprits.

Two greenhouse gases are carbon dioxide and methane. The former arises mainly from the burning of fossil fuels and the latter occurs during fermentation of organic waste. Using power point, a delightful picture was shown of people on a beach forming the figure 350. This was done to create awareness that carbon dioxide, in the concentration of 350 parts to one million, will produce a stable climate scenario. Unfortunately, in the world it is 390 parts per million. South African emissions per $GDP is the highest concentration in the world and twice the level of the rest of Africa. President Jacob Zuma has stated that by the year 2020 it should be reduced by 34% and by 2025 by 42%. This entails moving away from fossil fuels: roads generate 10% in the form of carbon dioxide, methane and small amounts of nitrous oxide. However, the main challenge is on Eskom and on popular support and co-operation to bring down demand for electricity. An interesting illustration showing 10 X 100 watt incandescent light bulbs burning for one hour, using 1 kilowatt hour of electricity, produces 1 kg of carbon dioxide. The same process by Eskom would require 1.4 litres of water, a very scarce resource in South Africa.

Other methods, tried worldwide, for generating electricity are:- Photo-Voltaic cells, concentrated solar plants using mirrors, wind generators (which leave no carbon footprint and use no water, but can be unpredictable), tidal streams and hydro energy from dams, and anaerobic digestion of organic waste producing gas for driving turbines.

In Cape Town 5000 tons of solid waste per day and 15000 tons of carbon dioxide are released. Landfall sites are filling up at an alarming rate. Compacted waste is presently sent to Vissieshoek and sewage waste is treated in digester units near Athlone. This plant deals with 560 million litres of water every day, which has to be treated before it can be safely disgorged into the rivers and sea. In the process it yields 850 kilograms of carbon dioxide per day.

In nature there is no evidence of waste creation. Everything has a part to play; dead leaves are absorbed into the soil and used in the growing process. An ant hill for instance presents an efficient scenario. We should do likewise. We should reduce waste by recycling glass bottles, melting down tin cans, using recycling materials for packaging and ultimately converting organic waste to methane for gas engines, cooking and for creating electricity—-ie “The marriage between waste and clean energy.

In parts of the northern hemisphere there is a move to a zero land fill policy. Thermal treatment by incineration, pyrolysis and gasification to produce electricity, wet anaerobic digestion from cow slurry, yield methane for use as above, while the waste residues yield nutrient rich fertilisers. In Germany biogas plants utilise biomethane to run a turbine for electricity and, in the USA, an array of microturbines.

Alastair presented two case studies, run by Agama, on the screen. Case 1—a set up for a rural housewife of a unit, using waste from toilets and cattle to generate gas for cooking and heating, and sludge for compost —thus relieving a lot of daily drudgery. Case2—(not yet in commission)on a larger scale for a township in Cato Manor— sewage is passed through a filter, then a biogas digester, which produces biogas (an energy source), solids for composting and liquids which pass into an algae pond for fish food. Although controversial, one square hectare of land could produce sufficient biomethane for a car to run for 67,000 km. Burning methane produces CO2+H20 and reduces the global warming potential by twenty one times and produces water and carbon dioxide used for photosynthesis by plants.

A most thought provoking lecture was followed by interested questions from the audience.